Use of polyamide as an encapsulating material for photovoltaic modules

ABSTRACT

Polyamide as an encapsulating material for the production of photovoltaic modules.

The invention relates to the use of polyamide as an encapsulating material for photovoltaic modules.

Photovoltaic modules are used to generate electrical power. In this case, part of the structure of photovoltaic modules comprises solar cells which, by exposure to sunlight, generate electrical charges which can be drawn off as current. Depending on the type, these solar cells are sensitive to mechanical influences or weathering influences to different extents. Encapsulating materials are used in order to protect said solar cells from these influences. These materials can consist of one or more layer(s), made of glass and/or plastic composites.

At the present time, composites of fluoropolymer materials and polyester (PET) are used as standard for encapsulating materials. A fluoropolymer layer on the outside guarantees weathering resistance, the PET film in the core guarantees the mechanical stability and the electrical insulation and another fluoropolymer layer on the inside guarantees the connection to the embedding material of the solar cells.

With these materials it is found that the adhesion to the embedding material, e.g. ethylvinyl acetate (EVA) is low. Furthermore, relatively thick composites are required to ensure the desired electrical insulation. This is attributable on the one hand to the low insulating capacity of fluoropolymer layers and on the other hand, to the adhesive layers used as standard between the films. The smallest irregularities or inclusions in the adhesive layers have the result that high currents flow in a punctiform manner. This phenomenon must be counteracted by a larger thickness of the PET film in the core as a precaution.

The present invention wishes to remedy this.

The use of polyamide as an encapsulating material for the production of photovoltaic modules is provided according to the invention.

The use of polyamide is advantageously effected as a film or as a film composite containing polyamide (PA). The advantageous use of a plastic composite is further proposed, said composite comprising a carrier material selected from the group of polyethylene terephthalate (PET), polyethylene naphthenate (PEN) or ethylene tetrafluoroethylene copolymer (ETFE), as well as polyamide-12 layers adjoining the carrier material on both sides.

The use of polyamide makes it possible to achieve very good adhesion to the embedding material which, as described above, can be, for example, EVA. In particular, the electrical insulation can be improved significantly by using a polyamide single film with the same thickness as compared to a composite comprising fluoropolymer layers and PET. It is not possible for high currents to flow in a punctiform manner via defects or inclusions in the adhesive layers.

Polyamide films can likewise be designed as weather- and UV-stabilised so that values comparable to those when using fluoropolymers can also be achieved with regard to these properties. Various colour combinations can also be adjusted by means of pigmentation. Furthermore, two production steps, i.e. the production of the PET/fluoropolymer layer composite and the fluoropolymer layer/PET/fluoropolymer layer composite can be saved.

Special standards relating to flame retardancy can be used for photovoltaic modules, in particular when mounted on roofs and integrated in buildings. Detailed explanations on this can be found in the standards of the Underwriter Laboratories UL94 and UL790. In order to be able to likewise use the advantages according to the invention of polyamide under these conditions, it is necessary to produce a composite with a fluoropolymer layer as a flame-retardant layer on the outside. Special applications can also necessitate the additional use of another film, e.g. made of polyethylene terephthalate, between the fluoropolymer layer and the PA film.

Further embodiments of the use according to the invention are disclosed in the patent claims.

The invention is explained in detail hereinafter with reference to possible embodiments—see FIGS. 1 to 5—as well as with reference to a possible exemplary embodiment.

FIG. 1 shows the exemplary structure of a photovoltaic module which is encapsulated with the material 1 used according to the invention. The encapsulating material 1 comprises a weather-resistant film which at the same time serves as an adhesion promoter to the embedding material 2. The embedding material 2 produces the non-positive connection to the solar cells 3 and to the embedding material 2′. The embedding material 2′ further ensures the non-positive connection to the encapsulating material 4.

FIG. 2 shows the exemplary structure of a photovoltaic module which is encapsulated with the material 1 used according to the invention. In contrast to FIG. 1, in this exemplary structure, the encapsulating material 1 is used on both sides of the solar cells 3.

FIG. 3 shows the exemplary structure of a photovoltaic module which is encapsulated with the material 1 used according to the invention. In order to satisfy additionally higher requirements on the flame retardancy such as prescribed, for example, in the corresponding standards UL94 and UL790, a fluoropolymer layer 5 is used as an additional layer to the encapsulating material 1 on the side facing away from the solar cells 3. In this exemplary design, the fluoropolymer layer 5 and the encapsulating material 4 thus constitute the respectively outermost layer of the photovoltaic module.

FIG. 4 shows the use according to the invention of a plastic composite 1, 1′ with the polyamide 12 layers 12 which are disposed on both sides of the carrier material 13. The carrier material consists of polyethylene terephthalate or polyethylene naphthenate or ethylene tetrafluoroethylene copolymer.

FIG. 5 shows a possible laminating device for producing a non-positive composite 6 from the materials 1 and 5 according to FIG. 3. The encapsulating material 1 which is selected according to the exemplary embodiment is coated with adhesive by means of the applicator unit 7 and after passing through a drier 10 is adhesively bonded to the fluoropolymer layer 5. The contact between the two films is controlled by the pressing pressure between the rollers 11. In this case, the material 1 can be pre-treated by means of physical media 9 before each production step.

The non-positive connection between the encapsulating material 1 and the fluoropolymer layer 5 can also be produced by co-extrusion. In this case, it is also possible to insert an adhesion promoter layer between the materials 1 and 5 and thus produce a triple-layer co-extrudate. The encapsulating material 1 itself can comprise a monolayer or likewise a co-extrudate of several layers.

Before using the encapsulating material 1 according to the invention or also before adhesive bonding with the fluoropolymer layer 5, the material 1 can be pre-treated by means of chemical or physical media. This pre-treatment can be implemented on one or also on both sides of the encapsulating material 1.

The following exemplary embodiment reproduces possible variants for the selection of the components in the respective layers:

Encapsulating material 1 as film: polyamides (PA) of the type polyamide 6, polyamide 66, polyamide 7, polyamide 9, polyamide 10, polyamide 11, polyamide 12, polyamide 69, polyamide 6 10, polyamide 6 12, PA-6-3-T, PA 6I, polyphthalamide (PPA) as well as other possible aromatic, partially aromatic and co-polyamides comprising these types.

Embedding material 2, 2′: ethylvinylacetate (EVA), polyvinylbutyral (PVB), ionomers, polymethylmethacrylate (PMMA), polyurethane, polyester, hotmelt or silicone elastomers.

Encapsulating material 4: glass

Fluoropolymer layer 5 as film: polyvinylfluoride (PVF), polyvinylidenefluoride (PVDF), ethylenechloro trifluoroethylene (ECTFE), polychlorotrifluoroethylene (PCTFE), ethylenetetra-fluoroethylene (ETFE), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene-vinylidenefluoride (THV), tetrafluoroethylene-perfluoroalkoxy-vinylether-copolymerisate (PFA), perfluoro-ethylene-propylene (FEP).

Fluoropolymer layer 5 as coating: fluoropolymer from the group of selectively soluble fluoropolymers.

The photovoltaic modules constructed from the aforesaid components are extremely stable when used outside which can be attributed, inter alia, to the good adhesion of polyamide to the embedding material. 

1. A photovoltaic module comprising solar cells encapsulated by polyamide.
 2. The photovoltaic module according to claim 1, characterised in that the polyamide is selected from the group polyamide 6, polyamide 66, polyamide 7, polyamide 9, polyamide 10, polyamide 11, polyamide 12, polyamide 69, polyamide 6 10, polyamide 6 12, PA-6-3-T, PA 6I, polyphthalamide (PPA).
 3. The photovoltaic module according to claim 1, characterised in that the polyamide is a copolymer of various aromatic or partially aromatic monomers.
 4. The photovoltaic module according to claim 1, characterised in that the polyamide is a monofilm.
 5. The photovoltaic module according to claim 1, characterised in that the polyamide is contained in a film composite.
 6. The photovoltaic module according to claim 1, characterised in that the polyamide is a colored monofilm or is contained in a colored film composite.
 7. The photovoltaic module according to claim 1, characterised in that the polyamide is a monofilm or is contained in composite film, and additives, preferably UV stabilisers, hydrolysis stabilisers, antioxidants, heat stabilisers or flame retardants are added to the polyamide film or the polyamide film composite.
 8. The photovoltaic module according to claim 1, characterised in that the polyamide is a monofilm or is contained in a film composite, which contains fillers.
 9. The photovoltaic module according to claim 4, characterised in that the polyamide film is pre-treated by means of physical media.
 10. The photovoltaic module according to claim 5, characterised in that the film composite contains a polyamide film and a fluoropolymer film.
 11. The photovoltaic module of a film composite according to claim 10, characterised in that the fluoropolymers are selected from the group polyvinylfluoride (PVF), polyvinylidenefluoride (PVDF), ethylenechloro trifluoroethylene (ECTFE), polychlorotrifluoroethylene (PCTFE), ethylenetetra-fluoroethylene (ETFE), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene-vinylidenefluoride (THV), tetrafluoroethylene-perfluoroalkoxy-vinylether-copolymerisate (PFA) or perfluoro-ethylene-propylene (FEP).
 12. The photovoltaic module according to claim 10, characterised in that the fluoropolymer film is coloured.
 13. The photovoltaic module according to claim 10, characterised in that the non-positive connection between the films is produced by an adhesive layer.
 14. The photovoltaic module according to claim 13, characterised in that the adhesive layer comprises a polyurethane or polyester adhesive.
 15. The photovoltaic module according to claim 13, characterised in that the non-positive connection between the films is produced by means of co-extrusion.
 16. The photovoltaic module of according to claim 15, characterised in that during the co-extrusion between the films additionally at least one adhesion promoter is extruded.
 17. The photovoltaic module according to claim 4, characterised in that the polyamide monofilm additionally comprises a fluoropolymer layer.
 18. The photovoltaic module according to claim 17, characterised in that the fluoropolymer layer contains selectively soluble fluoropolymers.
 19. The photovoltaic module according to claim 17, characterised in that the fluoropolymer layer is coloured.
 20. The photovoltaic module according to claim 17, characterised in that an adhesion promoter layer is located between the polyamide film and the fluoropolymer layer.
 21. The photovoltaic module according to claim 20, characterised in that the adhesion promoter is polyurethane and/or polyester and/or polyacrylate.
 22. The photovoltaic module according to claim 17, characterised in that a film of polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) is additionally provided between the polyamide film and the fluoropolymer layer.
 23. The photovoltaic module according to claim 22, characterised in that the non-positive connection is produced by adhesive layers.
 24. The photovoltaic module according to claim 23, characterised in that the adhesive is a polyurethane or polyester adhesive.
 25. The photovoltaic module according to claim 22, characterised in that the non-positive connection is produced by means of co-extrusion.
 26. The photovoltaic module according to claim 25, characterised in that during the co-extrusion additionally at least one adhesion promoter is extruded.
 27. A method of making the photovoltaic modules of claim 1, comprising encapsulating the solar cells with polyamide in combination with an embedding material selected from the group ethylvinylacetate (EVA), polyvinylbutyral (PVB), ionomers, polymethylmethacrylate (PMMA), polyurethane, polyester, hotmelt or silicone elastomers.
 28. The method according to claim 27, characterised in that the embedding material is applied to the polyamide by means of co-extrusion.
 29. The method according to claim 28, characterised in that an adhesion promoter layer is located between the polyamide and the embedding material.
 30. The method according to claim 29, characterised in that the adhesion promoter is single- or multi-layer and consists of polyurethane and/or polyester and/or polyacrylate.
 31. A photovoltaic material comprising solar cells encapsulated by a plastic composite comprising a carrier material selected from the group polyethylene terephthalate, polyethylene naphthenate or ethylene-tetrafluoroethylene copolymer as well as polyamide 12 layers adjoining the carrier material on both sides. 